1. Field of the Invention
The present invention relates to memory and computational devices based on quantum-mechanical interaction between individual bits. More particularly the present invention relates to solid-state devices comprising a ring structure as basic element for storing a single bit of information.
2. Description of the Related Art
During the last decade, quantum computing has become a topic of ever growing interest, particularly in the field of cryptography applications, based on Shor's algorithm for factoring large integers as disclosed by P. W. Shor in “Algorithms for quantum computing: discrete logarithms and factoring” in Proc. 35th Annual symposium on the foundations of computer science, 1994, pp 124-123, which is incorporated herein in its entirety by reference. This is due to the fact that the quantum-mechanical superposition principle allows for a level of parallel computing that exceeds all classical methods in this field.
A characteristic that differentiates quantum computing from classical computing is the entanglement of the bits. Also in classical computing devices operating at atomic scale is being developed. Although these “quantum devices” use discrete charge quanta the value of each bit is well defined: either a “0” or a “1”. In quantum computing however the interference between subsequent bits may bring the system in entangled multibit states, which are not accessible in classical computing.
All implementations of such a quantum computer starts with the design of an individual unit of information processing, the so-called quantum bit or “qbit”.
A first series of approaches addresses the design of this quantum bit at atomic level. The single qbit is realized e.g. as a spinning electron, an atomic nucleus or an oscillating molecule. Whereas these approaches directly address the quantum scale, they lack the connection of the qbit to the outside world: input/output structures (I/) ports are not easily available. PCT International Publication No. WO 00/30255, entitled “Crystal Lattice Quantum Computer”, published on May 25, 2002, which is incorporated herein in its entirety by reference, shows a crystal lattice computer where the qbit is associated with the orientation of the nuclear spin of the atoms.
A second series of similar approaches forms quantum systems but on a larger, nano- or mesoscopic, scale such as quantum dots, nanometer-sized rings or quantum wires. Although these devices are larger than the devices of the first approach, they operate similarly as if these devices where “artificial or macro-atoms”. Quantum dots are microscopic, carefully tailored regions of a semiconductor surface in which the number of electrons is precisely controlled. Axel Lorke et al. discloses in “Spectroscopy of nanoscopic semiconductor rings”, Phys. Rev Letter 84, March 2000, which is incorporated herein in its entirety by reference, the manufacturing of an array of semiconductor quantum rings starting from InAs droplets formed on a GaAs surface. The minute rings allow one or two electrons to circulate in coherent quantum states corresponding to one of the values of a bit. These quantum states are dependent on the applied large external magnetic field of about 8 Tesla, as was shown by externally providing energy in the form of infrared radiation having the appropriate wavelength to allow transitions between these magnetic-field-dependant quantum states. This external magnetic field is applied uniform over the nanoscopic ring as the rings are positioned in-between two parallel plates. Although the authors succeeded in forming qbits on an above-atomic scale, no mention of I/O ports is indicated and the proposed device are for research purpose only, without giving any information about integration, even of a single qbit, in a CMOS (complementary Metal Oxide Semiconductor) compatible technology.